Most hospitals have stopped testing all patients for SARS-CoV-2 upon admission and requiring masking. Ten hospitals in the Mass General Brigham hospital system ended both these precautions simultaneously in May 2023 but restarted masking for healthcare workers in January 2024 during a winter respiratory viral surge. Pak, et al. (2024) characterized the association of these changes with the relative incidence of hospital-onset SARS-CoV-2, influenza, and respiratory syncytial virus (RSV).

For this cohort study, the investigators analyzed all patients admitted between November 6, 2020, and March 21, 2024, to 10 hospitals (two tertiary hospitals, seven community hospitals, and one eye and ear hospital) using a Poisson interrupted time-series design. They identified hospital-onset infections (first positive polymerase chain reaction [PCR] test more than four days after admission) and community-onset infections (first positive within four days) for SARS-CoV-2, influenza, and RSV. The study had four periods: pre-Omicron with universal testing and masking; Omicron with universal testing and masking; Omicron without universal testing and masking; and Omicron after restarting masking for healthcare workers alone. Periods with universal testing included both admission testing and serial retesting of patients who were SARS-CoV-2-negative. Adherence to testing policy was assessed using systemwide testing data. The authors modeled level and trend changes in the rate of hospital-onset infections relative to community-onset infections across these periods and adjusted for seasonality and seasonality-period interactions.

They reviewed 100 randomly selected hospital-onset SARS-CoV-2 cases admitted after universal testing ended, to assess whether community-onset cases were being misclassified as hospital-onset using three yes or no characteristics: new symptoms of respiratory infection, known exposure to SARS-CoV-2, and PCR cycle threshold of less than 30. All analyses were performed in R version 4.2.1 (R Project for Statistical Computing). Data were analyzed from December 19, 2023, to October 7, 2024.

Among 641,483 admissions (357,263 women [55.7%]; median [IQR] age, 61 [38-74] years), there were 30 ,071 community-onset and 2,075 hospital-onset SARS-CoV-2, influenza, and RSV infections. While universal testing was in effect, admission SARS-CoV-2 tests were collected for 386,257 of 415,541 admissions (92.9%), compared with 39,765 of 149,712 admissions (26.5%) after stopping universal testing. The median (IQR) interval between tests in admissions of eight days or more was 4.4 (3.4-6.1) days during universal testing vs 11.1 days (8.4-17.0) days after stopping universal testing.

In unadjusted analyses, the mean weekly ratio between hospital-onset and community-onset infections increased from 2.9% prior to Omicron dominance to 7.6% (95% CI, 6.0%-9.1%) during Omicron dominance. After universal masking and testing ended, it increased to 15.5% (95% CI, 13.6%-17.4%), then fell to 8.0% (95% CI, 5.0%-11.0%) following resumption of masking among healthcare workers. Under the adjusted Poisson model, cessation of universal masking and testing was associated with a 25% increase in hospital-onset respiratory viral infections compared with the preceding Omicron-dominant period (rate ratio [RR], 1.25; 95% CI, 1.02-1.53), and resumption of masking among staff was associated with a 33% decrease in hospital-onset respiratory viral infections (RR, 0.67; 95% CI, 0.52-0.85).

Reference: Pak TR, et al. Testing and Masking Policies and Hospital-Onset Respiratory Viral Infections. JAMA Netw Open. 2024;7(11):e2448063. doi:10.1001/jamanetworkopen.2024.48063